The present invention relates to a honeycomb structure used in, for example, a carrier for a catalyst having a catalytic action, for use in an internal combustion engine, a boiler, a chemical reactor, a fuel cell reformer, etc., and to a filter for trapping fine particles present in an exhaust, and to an assembly thereof. More particularly, the present invention relates to a honeycomb structure that resists breaks when exposed to vibration or thermal stress during use, and to an assembly thereof.
Honeycomb structures are in use in, for example, a carrier for a catalyst having a catalytic action, for use in an internal combustion engine, a boiler, a chemical reactor, a fuel cell reformer, etc., and to a filter for trapping fine particles present in an exhaust gas, particularly fine particles emitted from a diesel engine.
In a honeycomb structure used for such a purpose, a sharp temperature change of exhaust gas and local heating makes non-uniform a temperature distribution inside the honeycomb structure, and there have been problems, such as crack generation, in the honeycomb structure and the like. When the honeycomb structure is used particularly as a filter for trapping a particulate substance in an exhaust gas emitted from a diesel engine, it is necessary to burn fine carbon particles deposited on the filter to remove the particles and regenerate the filter and, in that case, high temperatures are inevitably generated locally in the filter; as a result, a large thermal stress and cracks have tended to generate.
Hence, processes have been proposed for producing a honeycomb structure by bonding a plurality of individual honeycomb segments together using an adhesive. For example, U.S. Pat. No. 4,335,783 discloses a process for producing a honeycomb structure that comprises bonding a plurality of honeycomb parts using a discontinuous adhesive. Also, JP-B-61-51240 proposes a thermal shock-resistant rotary regenerating heat exchanging method that comprises (1) forming, by extrusion, matrix segments of honeycomb structure made of a ceramic material, (2) firing them, (3) making smooth, by processing, the outer peripheral portions of the fired segments, (4) coating the to-be-bonded areas of the resulting segments with a ceramic adhesive having, when fired, substantially the same chemical composition as the matrix segments and showing a difference in thermal expansion coefficient of 0.1% or less at 800° C., and firing the coated segments. Also, SAE article 860008 of 1986 discloses a ceramic honeycomb structure obtained by bonding cordierite honeycomb segments with a cordierite cement. Further JP-A-8-28246 discloses a ceramic honeycomb structure obtained by bonding honeycomb ceramic members with an elastic sealant made of at least a three-dimensionally intertwined inorganic fiber, an inorganic binder, an organic binder and inorganic particles.
Meanwhile, regulations for exhaust gas have become stricter, and engines have come to have higher performances. As a result, in order to achieve improvement in combustion conditions of an engine and an increase in the purification ability of a catalyst, the temperature of the exhaust gas has increased year by year. In this connection, a higher thermal shock resistance and a higher vibration resistance have come to be required for the honeycomb substrate. Therefore, even with honeycomb structures such as mentioned above, when the vibration, heat, exhaust gas pressure, etc., applied thereto during use becomes larger, it is possible that cracks, etc., will appear in the adhesive used therein or areas bonded therewith and, in an extreme case, there may occur, for example, disintegration of the honeycomb structure and breakage of the structure into fine pieces caused by vibration.
The present invention has been made in view of the above situation. It aims at providing a honeycomb structure having improved durability and resistance to damage caused by vibration, heat, exhaust gas pressure, etc., applied during use, and to the assembly thereof.